Glazing with electrical terminal

ABSTRACT

A glazing provided with an electric circuit includes an electrically conducting substrate and a terminal for making electrical connection thereto. The terminal is attached to the glazing by an adhesive, rather than solely by solder, and the electrical connection between the terminal and the substrate is provided by means other than, or additional to, physical contact between the terminal and the substrate. For instance, the adhesive may be electrically conducting, or a soldered joint may additionally be provided if the adhesive is electrically insulating, or of insufficient conductivity for the type of circuit in question. The adhesive may be pre-applied to the terminal, and may be a tack-free adhesive activated or cured by heat. The terminal may be in two parts, with the base part of a standardised design. The glazing is suitable for use in buildings, appliances or vehicles, especially automotive vehicles.

DESCRIPTION

[0001] The present invention relates to a glazing provided with anelectric circuit including an electrically conducting substrate and aterminal for making electrical connection thereto. In particular, thecircuit may be a heating element for defrosting or demisting theglazing, or an antenna circuit. The glazing may be for a vehicle window,or a window for an appliance or a building; in the case of a vehicle itmay be a windscreen or rear window.

[0002] Various techniques are known for making electrical connection toa terminal. For instance, it is known from GB-A-2 223 385 to solder aterminal to a busbar or current collector. Alternatively, EP-A-410 766discloses an electrical device comprising a substrate supporting afilm-type heater track formed of conductive polymer ink. A connectormember is bonded to the substrate by means of adhesive, and the heatertrack overlies at least an end portion of the connector member toprovide an electrical contact between them.

[0003] It is also known from EP 278 611 A1 to employ an electricallyconductive adhesive to bond a busbar onto a conductive layer formed on asubstrate, which may be used as a window. Furthermore, in GB 1 393 887,the use of steel filings to make electrical contact through an adhesivecoating is disclosed in the context of a rear window heating circuit.

[0004] However, FR 2 519 477 teaches that electrically conductiveadhesives have various disadvantages, for example, they are notsufficiently durable under the conditions to which a vehicle window istypically subjected, and they are expensive. Instead, FR 2 519 477suggests that it is preferable to employ a non-conductive adhesive tomaintain a suitably configured terminal in intimate contact with anelectrically conducting substrate so as to ensure electrical continuity.

[0005] Unfortunately, the invention of FR 2 519 477 is also not withoutdisadvantages; it has been found that the inevitable mismatch of thethermal expansion coefficients of glass, metal and adhesive results in aweakening of the adhesive bond to the extent that electrical contact isadversely affected. Consequently, soldering remains a widely usedtechnique for attaching electrical terminals to glazings, although thestrength of the bonds produced is not always satisfactory, and there areincreasing environmental concerns about metals, such as lead, which arecommonly used in solders. Furthermore, the actual soldering operation isinclined to produce thermal stresses in the glass, which sometimes leadto damage.

[0006] It would be desirable to improve the attachment of electricalterminals to glazings, avoiding the disadvantages described above.

[0007] According to the present invention there is provided a glazingwith an electric circuit including an electrically conducting substrateand a terminal for making electrical connection thereto, wherein theterminal is attached to the substrate by adhesive, characterised in thatthe electrical connection between the terminal and the substrate isprovided by means other than, or additional to, physical contact betweenthe terminal and the substrate.

[0008] The provision of a secure and reliable electrical connectionbetween the terminal and the substrate allows adhesives to replacesolder without attendant problems of electrical continuity. Modernadhesives are able to offer many advantages over solder. They may beflexible in the cured or set condition, and thereby absorb stressesgenerated in, or exerted on, the terminal. Adhesives are available whichdo not require to be heated in order to form a bond, or only need to beheated to a modest temperature, and yet which still provide a strongbond. Furthermore, it is usually possible to arrange the manufacturingoperation so that the adhesive is heated just before it contacts theglazing, thereby avoiding the need to heat the glazing directly. Durableelectrically conducting adhesives are now available, thereby allowing,the adhesive to fulfil both the mechanical and electrical functions of aconventional soldered joint. Generally, such adhesives contain finelydispersed metal powder to make them conductive. Providing that theelectric current to be carried is not large, the adhesive constitutes asufficient electrical connection. A further important advantage is thatsuitable adhesives are available which have fewer health and safetyhazards and less adverse environmental impact than the conventionallyused solders.

[0009] Preferably the terminal comprises separate base and connectorparts which are adapted to mutually engage, and the base part of theterminal is attached to the glazing by adhesive.

[0010] Advantageously, especially in the automotive industry, the basemay be of a standardised design of general applicability, whereas theconnector part may be tailored to the specific requirements of aparticular glazing, vehicle or vehicle manufacturer. That is, the baseis preferably usable with a variety of differing designs of connectorpart.

[0011] Means of electrical connection between the terminal and thesubstrate may, for example, include the use of an electricallyconducting adhesive, and/or a soldered connection. In high currentapplications, a joint soldered directly between the terminal and thesubstrate is preferable as the additional means of electricalconnection, in order to obtain a low resistance connection. In thissituation the solder complements the adhesive, as the latter bears themechanical load and stresses, leaving the solder to provide, or enhance,electrical continuity without being compromised. This makes it possible,for instance, to use solders which are less environmentally aggressive,even if there is some loss in bond strength.

[0012] The invention also provides a method of making a glazing with anelectric circuit including an electrically conducting substrate and aterminal for making electrical connection thereto, comprising the stepsof:

[0013] providing a pane carrying the electric circuit and substrate, and

[0014] attaching the terminal to the substrate with adhesive,characterised by

[0015] providing the electrical connection between the terminal and thesubstrate by means other than or additional to, physical contact betweenthe terminal and the substrate.

[0016] Improvements can also be made in the type and method ofapplication of the adhesive.

[0017] Preferably the adhesive is provided in the form of a tack-freetablet which is placed in contact with the terminal. The use of atack-free (i.e. non-sticking) form of adhesive is advantageous becausehandling of the adhesive is greatly facilitated.

[0018] It is also preferable for the adhesive to be pre-shaped to matchthe part of the terminal that the tablet is in contact with. Thisincreases the area of the terminal that is bonded, and hence thestrength of the bond, while reducing the likelihood of adhesive escapingfrom underneath the terminal and becoming visible, which is likely to beunsightly. It also results in less waste and hence a cost reduction.

[0019] Advantageously the adhesive is pre-applied to the terminal, e.g.the terminals may be supplied with adhesive already applied to therequisite part of the terminal.

[0020] Optionally the adhesive may be heated to activate or cure it. Theterm “activating” an adhesive is used to refer to any process whichinitiates the bonding process, e.g. one which makes a previouslytack-free adhesive sticky, or one which starts the curing process.Activation may involve melting the adhesive (at least on its surface),initiating a heat-dependent chemical reaction, or removing or destroyinga barrier which separates two reactants. The extent of heating anadhesive is frequently less than is required for solder, and with regardto heating for activation, the adhesive need not necessarily be incontact with the glazing at the time of heating.

[0021] In this specification, the 'term “solder” is used to denote afusible alloy of metals. The term “adhesive” is used to denote asubstance employed to bond other substances together, but does notinclude a solder as such. An adhesive may be wholly non-metallic or maycontain a metallic component.

[0022] The invention will now be further described by way of thefollowing specific embodiments, which are given by way of illustrationand not of limitation, and with reference to the accompanying drawingsin which:

[0023]FIG. 1 is a perspective view of part of a glazing which includesan electric circuit and has a terminal attached;

[0024]FIG. 2 is a perspective view of a terminal which comprisesseparate base and connector portions;

[0025]FIG. 3 is a perspective view of a one-part terminal;

[0026]FIG. 4 is a plan view of the terminal of FIG. 3; and

[0027]FIG. 5 (a)-(c) are perspective views of preshaped tablets ofadhesive.

[0028]FIG. 1 illustrates a glazing 1 including an electric circuit 2. Inthis case the electric circuit is a resistive heating circuit printed ona pane 3 of glazing material in a conductive ink. Such circuits are usedfor defrosting and demisting, e.g. in vehicles, and as they are wellknown they need not be described further. Other equally well-knownheating circuits comprise fine wires or a thin electroconductive coatingon the pane. Alternatively the circuit may be an antenna circuit, againas is well-known.

[0029] The pane 3 of glazing material may be a sheet of glass, which maybe annealed or toughened, or a composite pane made up of two or moreplies of glass (or other glazing material) laminated together. In thecase of an automotive glazing, the glass would be safety glass, i.e.toughened or laminated glass. There are alternative glazing materials toglass including various plastics such as polycarbonate for example.

[0030] Attached to the glazing, or more precisely, to an electricallyconducting substrate 4 which forms part of the-electric circuit 2, is aterminal 5. The embodiment of terminal 5 shown in FIG. 1 comprises abase part 6 and an upper (as illustrated) or connector part 7, which areadapted to mutually engage, as will be explained in more detail below inconnection with FIG. 2. The base part 6 is attached to the glazing 1 byadhesive 8, again as will be explained in more detail below. Theterminal may be in intimate physical contact with the substrate, butthis is not necessary since an alternative means of electricalconnection is provided, as described below.

[0031] In this embodiment, the electrically conducting substrate 4constitutes a busbar supplying current to heating elements of theelectric circuit 2. The suhstrate may be composed of thin sheet metal,such as a foil, or may be made from an ink which is applied to the pane(e.g. by screen printing), dried, and fired to provide a durableconducting path. For example, silver-containing inks are widely used inthe manufacture of electrically heated rear windows for vehicles.

[0032] The terminal 5 includes a spade connector 9, to which anelectrical lead (not shown) may be attached in conventional fashion by acorresponding female connector. Many variations on the type andembodiment of connector are possible; for example, it may be cranked, orotherwise bent, to facilitate access or to improve its aesthetic aspect.Alternative forms of connector, e.g. the press stud type, may also beused. The terminal may be manufactured from thin sheet metal; inparticular, copper sheet, preferably tinned to prevent oxidation, is asuitable material.

[0033]FIG. 2 shows more details of the terminal 5. As already mentioned,the terminal 5 comprises a base part 6 and a connector part 7, which areadapted to mutually engage each other. For example, base part 6 may beprovided with tabs 20, which are bent around the connector part 7, e.g.around the spade 9.

[0034] It has already been mentioned that it is convenient for theterminals to be supplied with the adhesive preapplied, especially in atack-free form. The tablet of adhesive (generally comprising pre-mixedcomponents) is pressed onto the surface of the terminal with justsufficient heat to cause it to adhere to the surface. When the terminalis in two (or more parts) as in FIGS. 1 and 2, it is especiallyconvenient for the base part 6 to be of a standard universal design,with the adhesive pre-applied to it. This means that only one design ofbase part need be purchased, which is then used with a connector partwhich suits the particular vehicle glazing being manufactured. The basepart may either be attached to the glazing first, or to the connectorfirst, whichever is more convenient. In FIG. 2, a tablet of adhesive 8is applied to the terminal base part 6, as indicated by arrow A. Thebase part is then attached to the connector part 7 by means of tabs 20,as indicated by arrow B. Finally the terminal is attached to theglazing, as will be described below.

[0035] The adhesive may be electrically conducting, in which case nofurther electrical connection may be necessary. However, if the adhesiveis non-conducting, or if the electric circuit has a high powerrequirement, a means of electrical connection will be required betweenthe terminal and the electric circuit. This may conveniently be providedby a soldered joint between the terminal and the electrically conductingsubstrate. In FIG. 2, the application of solder is diagrammaticallyrepresented by arrows C and solder 21. For an antenna, which of courseonly produces a very small current, the use of a conducting adhesive mayoften provide sufficient electrical connection.

[0036]FIG. 3 shows an alternative embodiment of terminal 30. This is aone-part terminal, i.e. it is a single piece, and it corresponds to theconnector part 7 of the terminal of the first embodiment. The terminalis attached to the glazing by means of adhesive 8; preferably a tabletof tack-free adhesive is used as described above. The tablet may beapplied to the terminal as indicated by arrow D. Again, an auxiliaryconnection may be made with solder 21.

[0037]FIG. 4 shows the one-part terminal 30 in plan view, with adhesive8 and solder 21 applied. It is advantageous for the tablet of adhesiveto be positioned near the base of the spade connector 40, where it canresist any bending moment created during application of a correspondingfemale connector to the male spade 40, when the spade can act as alever. The solder joint is thereby protected from damage.

[0038]FIG. 5 (a)-(c) show shaped tablets 50, 51, 52 of adhesive, thetablet being pre-shaped to suit the shape of the terminal. Pre-shapingreduces waste, improves conformity to the terminal surface and improvesflow control during application of adhesive. A stronger and neater bondis thereby obtained, and this technique may be used with eitherembodiment of terminal.

[0039] In FIG. 5(a), a T-shaped block 50 of adhesive is shown, which issuitable for use in the correspondingly T-shaped part of the terminal(i.e. where the limbs of the “T” cross, one limb being the spade). FIG.5(b) shows a thin rectangular block 51 of adhesive and FIG. 5(c) shows athin cylindrical tablet 52 of adhesive.

[0040] There are many suitable adhesives for attaching terminals toglazing. Polyurethanes are a suitable class of adhesives, includingmoisture-cured polyurethane (e.g. Betaseal HV3 available fromGurit-Essex AG of Freienbach, Germany), moisture/heat cured polyurethane(e.g. Sika 360 HC available from Sika AG of Switzerland), reactive hotmelt polyurethane (e. g, PUR-FECT 310 available from National Starch &Chemical Company of Bridgewater, N.J., USA, a member of the ICI Group),two component polyurethane, and other polyurethane-based compositions(such as Techbond PUR available from A. Raybond SARL of 68300Saint-Louis, France) . A further suitable class of adhesives is that ofepoxy based compositions, e.g. Raybond's Techbond EPO. Also suitable arestructural adhesive tapes (e.g. 3M 9214 available from the MinnesotaMining and Manufacturing Company of St. Paul, Minn., USA). Suitableconducting adhesives contain finely dispersed metallic particles insufficient quantity to pass the required current density.

[0041] The preferred tack-free adhesives in tablet form are availablefrom A. Raybond SARL in both epoxy and polyurethane compositions(Techbond EPO and PUR), and terminal base parts can be supplied with theadhesive pre-applied. In a polyurethane-based composition such asTechbond PUR, the polyol and isocyanate reactants are pre-mixed instoichiometric ratio, but the isocyanate is “end capped” ormicro-encapsulated to prevent contact with the polyol. The adhesive issolid at room temperature. Application of heat activates the adhesive bydestroying, e.g. melting, the capping or encapsulating membrane andallowing the isocyanate component into contact with the surroundingpolyol so that the curing reaction starts. The method of use of theseadhesives is as follows.

[0042] A pane of glass carrying an electric circuit is provided andcleaned with a cleaner such as Betaseal VP04604 from Gurit-Essex; aterminal, or terminal base part, with tack-free adhesive pre-applied isalso provided. The terminal is positioned over the pane, and rapidlyheated to a temperature in the range 100°-140° C. Suitable rapid heatingtechniques include infra-red lamps, hot air jets, inductive heating orradio frequency dielectric heating. The heat activates the adhesive, andthe terminal is pressed into position on the pane. During the initialcooling period the terminal should be held in place, until thetemperature has reduced to a value in the region of 60°-80° C. The panemay then be moved, but the bond does not develop full strength untilpost polymerisation has been completed, which may require up to 20minutes at room temperature. Note that the pane need not be directlyheated, thereby reducing thermal stresses.

[0043] As mentioned above, in many cases it will be necessary to make aseparate electrical connection between the terminal and the circuit, anda preferred method involves soldering. In this case, the heat ofsoldering may advantageously also be used to activate the adhesive andeliminate a separate operation. The locations on the terminal body towhich solder is applied should be close to those to which adhesive isapplied. A soldering tool (which may be automated, e.g. robotcontrolled)is then used to solder the terminal in position, and simultaneously heatthe adhesive to activate it. The soldering tool may be one whichcontacts the work, or a hot air soldering technique may be used.Generally, soldering requires a higher temperature than activation ofthe adhesive, so the temperature attained may be governed by solderingconsiderations. However, one of the advantages of the invention is thatthe mechanical bond is provided by the adhesive, so that the soldersolely provides an electrical connection. Consequently, solders may beused which have a lower melting point than those used in the prior art,where both mechanical and electrical considerations apply.

[0044] In practice, certain types of adhesive are activated by meltingthem, and so the heat used to melt the solder preferably also melts theadhesive. It is therefore advantageous to select an adhesive and asolder which have similar melting points. Suitably, the adhesive andsolder have melting points within 20° C., preferably 10° C., mostpreferably 5° C. of each other.

1. A glazing (1) provided with an electric circuit (2) including anelectrically conducting substrate (4) and a terminal (5, 30) for makingelectrical connection thereto, the glazing comprising a pane (3) ofsheet glazing material which carries the electric circuit, wherein theterminal is attached to the substrate by both adhesive (8) and solder(21), such that the adhesive bears the mechanical load on the terminaland the solder provides the electrical connection between the terminaland the substrate.
 2. A glazing as claimed in claim 1, wherein theterminal comprises separate base and connector parts (6,7) which areadapted to mutually engage, and the base part (6) of the terminal isattached to the substrate by adhesive.
 3. A glazing as claimed in claim1 or claim 2, wherein the adhesive is one which is activated or cured byheat.
 4. A glazing as claimed in any preceding claim, wherein theadhesive is electrically conducting.
 5. A glazing as claimed anypreceding claim, wherein the adhesive and solder have melting pointswithin 20° C., preferably 10° C., most preferably 5° C. of each other.6. A glazing as claimed in any preceding claim, characterised in thatthe electrically conducting substrate is made from an ink which isapplied to the glazing, dried, and fired to provide a durable conductingpath.
 7. A method of making a glazing (1) provided with an electriccircuit (2) including an electrically conducting substrate (4) and aterminal (5, 30) for making electrical connection thereto, comprisingthe steps of: providing a pane (3) of sheet glazing material carryingthe electric circuit and substrate, and attaching the terminal to thesubstrate with both adhesive (8) and solder (21), such that the adhesivebears the mechanical load on the terminal and the solder provides theelectrical connection between the terminal and the substrate.
 8. Amethod as claimed in claim 7, wherein the adhesive is provided in theform of a tack-free tablet which is placed in contact with the terminal.9. A method as claimed in claim 8, wherein the tablet is pre-shaped tomatch the part of the terminal that the tablet is in contact with.
 10. Amethod as claimed in any one of claims 7 to 9, wherein the adhesive ispre-applied to the terminal.
 11. A method as claimed in any one ofclaims 7 to 10, wherein the adhesive is heated to activate or cure it.12. A method as claimed in any one of claims 7 to 11, wherein the heatof soldering also activates or cures the adhesive.
 13. A method asclaimed in any one of claims 7 to 12, wherein the electricallyconducting substrate is made from an ink which is applied to theglazing, dried, and fired to provide a durable conducting path.